Positive photoresists that use alkali-soluble resins and sensitizers such as 1,2-naphthoquinone diazide compounds have been known to serve as resists for manufacturing semiconductors such as ICs and LSIs, display devices such as LCDs, and plates for printing. There has been proposed a positive photoresist composition that uses a mixture of an m-cresol novolac resin and a p-cresol novolac resin as the alkali-soluble resin (for example, refer to PTL 1).
The positive photoresist composition described in PTL 1 was developed to improve the developing properties, such as sensitivity. However, the recent increase in the degree of semiconductor integration has required ever higher sensitivity to form patterns with finer lines. The positive photoresist composition described in PTL 1 has a problem in that it does not have sensitivity sufficient for forming finer lines. Meanwhile, coating films made from positive photoresist compositions need to withstand heat since they are subjected to various heat treatments in the steps of manufacturing semiconductors and the like. However, the positive photoresist composition described in PTL 1 has another problem in that it does not have sufficient heat resistance.
There has also been proposed a positive photoresist composition from which a coating film having heat resistance and high resolution can be obtained. In this composition, a polyhydroxyl compound such as 2,3,4-trihydroxybenzophenone is used as a sensitivity enhancer and a novolac resin obtained by adding oxalic acid to a mixture of 2,3-xylenol, m-cresol, p-cresol, and dihydroxybenzaldehyde to allow reaction of 2,3-xylenol, m-cresol, p-cresol, and dihydroxybenzaldehyde to thereby obtain a condensate (random polymer) and allowing the condensate to react with formaldehyde is used as a main ingredient (for example, refer to PTL 2 and PTL 3). However, none of the positive photoresist compositions described in PTL 2 and PTL 3 sufficiently meets the high level of heat resistance required in recent years.